1. Field of the Invention
The present invention relates to a lubricant for a compression type refrigeration system using ammonia refrigerant that does not have the possibility of ozone layer depletion and global warming. Further, the present invention relates to a working fluid composition comprising the ammonia refrigerant and the lubricant, and a refrigeration system which is filled with the working fluid composition.
2. Description of the Related Art
A compression type refrigeration system is composed of a compressor, a condenser, an expansion mechanism (such as an expansion valve or a capillary tube), an evaporator and so forth, and conducts cooling by utilizing a property of a refrigerant with high volatility which takes latent heat from its surroundings during evaporation. The compression type refrigeration system is used in a refrigerator, a freezer, an air conditioner, a showcase, a vending machine of soft drinks or ice creams, and the like. In air conditioner, vending machine or the like, the system is also used as a heater to warm the air, or drinks and foods by utilizing heat generated by condensing.
As the refrigerant, (hydro) fluorocarbons containing chlorine (CFC or HCFC) have conventionally been used. Recently, CFC or HCFC is being replaced by hydrofluorocarbons (HFC) not containing chlorine. However, CFC and HCFC break an ozone layer, and HFC has a high global warming ability. In view of earth environment protection, refrigerants that do not adversely-affect environment are desired as alternates of those hydrofluorocarbons. As a result, refrigerants such as low molecular weight hydrocarbons or ammonia, which do not break an ozone layer and have much smaller global warming ability than the above hydrofluorocarbons, become reevaluated as environment-friendly refrigerants. In particular, ammonia has high coefficient of performance.
Mineral oils or alkylbenzenes have been used as a base oil for a lubricant for a refrigeration system using an ammonia refrigerant. Recently, polyether compounds having compatibility with ammonia are proposed (for example, European Patent No. 490810A, European Patent No. 585934A, German Patent No. 4404804A and International Patent WO 95/12594A). By using a polyether compound having a compatibility with ammonia, there is the advantage that it is not necessary to provide a lubricant circulation facilities that separate and recover a lubricant at a discharge side of a refrigerating compressor, and return the recovered lubricant to the compressor.
However, ammonia as a refrigerant is a compound having high activity, it reacts with a base oil or additives of a lubricant for a refrigeration system, or deteriorated materials thereof to form separation substances (reaction products). As a result, there is fear of plugging of an expansion valve or capillary, abrasion of a sliding member, and further promoting deterioration of the lubricant. Further, ammonia has high corrosion property to a metal, particularly under the presence of water, and by using it with a polyether compound having high hygroscopicity, corrosion and deterioration of a metal, such as rust, are promoted. Further, because ammonia refrigerant requires high pressure operation compared with flon type refrigerant, refrigerant and lubricant are exposed to severer conditions such as high temperature and high pressure, and sliding conditions also become hard. As a result, there are the possibilities of increase of formation of separation substances, promotion of deterioration of lubricant (base oil and additives), and increase of friction and abrasion. Lubricants that have high lubricating properties including stability even under the severe condition using ammonia refrigerant are desired.
Regarding polyether compounds, derivatives of polyether compounds in which its terminal hydroxyl group is substituted with alkyl group or acyl group to improve stability and hygroscopicity (hereinafter referred to xe2x80x9cpolyether compoundsxe2x80x9d including derivatives) are proposed. However, the step producing the derivatives is added, and it brings the disadvantage such that good compatibility with ammonia lowers. Thus, the degree of improvement in stability and hygroscopicity are not sufficiently satisfied, and there is a limit to resolve by a base oil only. Therefore, it is required to select and use an appropriate additive in the combination of ammonia and a base oil. However, in many cases, additives have higher activity than base oil, more easily react with ammonia, and may promote deterioration and formation of separation substance.
An object of the present invention is to provide a lubricant having excellent compatibility with ammonia and having excellent performances of good stability and lubricating properties for practical use, as a lubricant for a refrigeration system using ammonia refrigerant.
The present invention has solved the above-mentioned various problems and achieved the the expected results. That is, the present invention provides a lubricant for a compression type refrigeration system using ammonia as a refrigerant, and the lubricant comprises (A) at least one kind of polyether compounds, and (B) at least one kind of aromatic amine compounds or phenothiazine compounds, and the lubricant preferably further comprises (C) at least one kind of alcohol compounds selected from the group consisting of oleyl alcohol, polyhydricalcohol partial ester and polyhydricalcohol partial ether, and/or (D) at least one kind of benzotriazole compounds selected from benzotriazole and its derivatives.
The present invention further provides a working fluid composition for a compression type refrigeration system, comprising the lubricant and ammonia refrigerant.
The present invention further provides a refrigeration system which is filled with the working fluid composition.
The polyether compounds (A) used in the present invention are used as a base oil that is the main component of a lubricant. Though they include various compounds, the polyether compounds may be used by appropriately selecting according to the purpose of use or the like. The preferable compounds include polyether compounds represented by the following formula (1):
X[xe2x80x94Oxe2x80x94(AO)n-R]mxe2x80x83xe2x80x83(1)
where X shows a hydrocarbon group in the form of excluding hydroxyl group from monool or polyol, A shows an alkylene group having 2-4 carbon atoms, R shows hydrogen or an alkyl group having 1-10 carbon atoms, m is a valence number of X, and n is a positive integer of 2 or more.
In the above formula (1), if X is a hydrocarbon group in the form of being derived from monool, X is preferably a straight-chain or branched-chain, saturated or unsaturated hydrocarbon group having 1-20 carbon atoms, and further preferably an alkyl group having 1-8 carbon atoms. Specific examples of the preferred monool include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol and octanol. If X is in the form of being derived from polyol, X is preferably a hydrocarbon group in the form of removing all hydroxyl groups from divalent to hexavalent polyol having 2-15 carbon atoms. Specific examples of the polyol include ethylene glycol, propylene glycol, glycerol, trimethylol ethane, trimethylol propane, trimethylol butane, pentaerythritol, sorbitan, sorbitol, and the like. Condensation type polyols such as diglycerol or dipentaerythritol may be used.
If the valence number m of X becomes large, the molecular weight of the polyether compound increases and its viscosity is too high, so that there is the tendency that compatibility with ammonia lowers. Therefore, the valence number m of X is preferably 1, 2 or 3. Of those, the valence number m of 1, that is, a hydrocarbon group in the form of being derived from monool, is particularly preferable as X. Even in such a hydrocarbon group, if the number of carbon atoms increases, viscosity becomes too high, compatibility lowers. Therefore, the carbon number of X is preferably 1-8 as mentioned above, more preferably 1-4. The most preferable X is methyl group. As X is a hydrocarbon group in the form of removing hydroxyl group from monool or polyol, X may include alcohol (monool or polyol) derivatives such as sodium alcoholate or potassium alcoholate, or compounds derived from alkylene oxide. Further, R represents hydrogen or an alkyl group having 1-10 carbon atoms. In the case that m is 2 or more, a plurality of R, i.e., a plurality of hydrogen and alkyl groups, can be present in one molecule. In this case, R may be only hydrogen atoms, or only the same alkyl groups, and may be a combination of hydrogen (S) and alkyl group (S), different alkyl groups, or hydrogen (S) and a plurality of different alkyl groups.
In the case that R is hydrogen, the compound is a polyether compound having hydroxyl group at the terminal. In the case that R is alkyl group, the compound is a polyether compound in which the terminal thereof is blocked by alkyl group. The polyether compound having hydroxyl group at the terminal has excellent compatibility with ammonia, on the other hand, a compound having alkyl group at the terminal has excellent stability. If the carbon number of alkyl group (R) decreases, there is the tendency that compatibility is improved. Therefore, among alkyl group, the carbon number is preferably 1-4, and methyl group is most preferable.
Further, A represents an alkylene group having 2-4 carbon atoms, i.e., ethylene group, propylene group and/or butylene group. Alkylene groups of (n X m) presenting in one molecule may be the same, or may contain two kinds or three kinds of the above-mentioned alkylene groups. Therefore, (AO)n (polyoxyalkylene group) of m can be obtained by polymerizing after appropriately selecting one kind or two kinds or more from ethylene oxide, propylene oxide and butylene oxide. In the polyoxyalkylene group, the proportion of each oxyalkylene group is not particularly limited. However, in the case of only one kind, oxypropylene group (PO) is preferable, and in the case of two kinds or more (copolymerization), it is preferable at least to contain oxyethylene group (EO) for ensuring compatibility. However, if the proportion of oxyethylene group increases, hygroscopicity increases, and it may be observed that pour point heightens and solidification occurs at room temperature. The proportion of the number of oxyethylene groups (EO) to the total number of oxyalkylene groups (AO) is preferably 50% or less, more preferably 10-30%. Further, in the case of copolymerization, the kind of polymerization may be any of block polymerization, random polymerization, or a combination thereof. However, in view of low temperature characteristics such as flowability, random polymerization or polymerization at least partially containing random polymerization is preferable.
In the above formula, the degree of polymerization of oxyalkylene group (AO), n, is an integer of 2 or more, and may appropriately be adjusted so as to obtain a polyether compound having appropriate viscosity and molecular weight. The integer n is preferably 2-150, more preferably 5-100. There is the tendency that the molecular weight of polyether is generally in direct proportion to the viscosity. The molecular weight and viscosity of the polyether compound represented by the formula (1) used in the present invention are not particularly limited. However if the viscosity decreases, sealing property deteriorates and lubricity also lowers. Whereas, if the viscosity increases, compatibility lowers and energy-saving property decreases. Therefore, kinematic viscosity at 40xc2x0 C. of the polyether compound is preferably 15-200 mm2/s, more preferably 20-150 mm2/s. The molecular weight is preferably about 300-3000. The polyether compound having such a viscosity and molecular weight can be obtained by appropriately adjusting X, A, R, m and n in the formula (1).
Aromatic amine compound or phenothiazine compound as another component (B) contained in the lubricant for a refrigeration system of the present invention is used as one of additives, and prevents oxidation of the lubricant. Generally, as an antioxidant for a lubricant other than compounds of component (B), phenol type, sulfur type, zinc thiophosphate type antioxidant and the like are known. However, those antioxidants are not necessarily effective as additives for a lubricant for a refrigeration system using ammonia refrigerant. Phenol type antioxidants have the problem forming separation substances by reacting with ammonia and then plugging capillary or the like. Further, sulfur type and zinc thiophosphate type antioxidants have the problem on corrosion, and there is the possibility that separation substances or rusts are formed to promote deterioration of a lubricant, thereby plugging capillary or expansion valve. To the contrary, the aromatic amine compound or phenothiazine used in the present invention is a chemically similar compound to ammonia of a refrigerant, and has high affinity and good compatibility with ammonia.
Specific examples of the aromatic amine compound or phenothiazine compound include dipyridylamine, phenothiazine, phenothiazine derivatives in which alkyl group is added to phenylene group, dialkyldiphenyl amine, diphenyl-p-phenylenediamine, diphenyl-p-phenylenediamine in which phenyl group is substituted with naphthyl group, alkyl group or the like, and dialkylphenyl-p-phenylenediamine, and the like. Of those, dipyridylamine, p,pxe2x80x2-dialkyldiphenylamine having alkyl group having 4-20 carbon atoms, preferably 4-12 carbon atoms, more preferably 8 carbon atoms, and N,N-dialkylphenyl-p-phenylenediaminehavingalkyl group having 2-20 carbon atoms, more preferably 4-12 carbon atoms, are preferable.
The addition amount of the aromatic amine compound or phenothiazine compound is preferably 0.01-5.0% by weight, more preferably 0.05-1.0% by weight, on the basis of the whole lubricant for a refrigeration system. If the addition amount is small, effect as an antioxidant is not obtained, on the other hand, if it is added exceeding 5.0% by weight, improvement in effect corresponding to the addition amount is not observed, this is not economical. Further, as it is observed that the oil tends to color by adding in large amount, excessive addition should be avoided.
The lubricant for a refrigeration system of the present invention, preferably further comprises (C) at least one kind of alcohol compound selected from the group consisting of oleyl alcohol, polyhydricalcohol partial ester and polyhydric alcohol partial ether, and/or (D) at least one kind of benzotriazole compounds selected from benzotriazole and its derivative, other than the above-mentioned aromatic amine compound or phenothiazine compound, as additive.
Further, it is preferable to use one kind or two kinds or more of any compounds of oleyl alcohol, polyhydric alcohol partial ester and polyhydric alcohol partial ether as component (C) in order to particularly improve abrasion resistance. Of those, polyhydric alcohol partial ester and polyhydric alcohol partial ether are preferable.
The polyhydric alcohol partial ester is a compound represented by the following formula (2);
R4(OH)p[OC(O)R5]qxe2x80x83xe2x80x83(2)
where R4 represents straight-chain or branched-chain, and saturated or unsaturated hydrocarbon group having 2-12 carbon atoms, corresponding to a residue of (p+q)-valent polyhydric alcohol, R5 represents straight-chain or branched-chain, and saturated or unsaturated hydrocarbon group having 3-20carbon atoms, p is the number of hydroxyl groups remaining unesterified, q is the number of esterified acyl groups, and p and q are integers satisfying 1xe2x89xa6p less than 6, 1xe2x89xa6q less than 6 and 2xe2x89xa6p+q less than 6. More specifically, it is a partial ester of a polyhydric alcohol such as glycol, glycerin, trimethylol propane, pentaerythritol, sorbitan or sorbitol, and a straight-chain or branched-chain, saturated or unsaturated fatty acid having 4-21 carbon atoms. Of those, a partial ester of glycerin, sorbitan or sorbitol, and fatty acid having 10-20 carbon atoms is preferable, fatty acid monoester is more preferable, and fatty acid monoester of glycerin is particularly preferable.
The polyhydric alcohol partial ether is a compound represented by the following formula (3);
R6(OH)r(OR7)sxe2x80x83xe2x80x83(3)
where R6 represents straight-chain or branched-chain, and saturated or unsaturated hydrocarbon group having 2-12 carbon atoms, corresponding to a residue of (r+s)-valent polyhydric alcohol, R7 represents straight-chain or branched-chain, and saturated or unsaturated hydrocarbon group having 3-20 carbon atoms, r is the number of hydroxyl groups remaining unetherified, s is the number of etherified ether bonds, and r and s are integers satisfying 1xe2x89xa6r less than 6, 1xe2x89xa6s less than 6 and 2xe2x89xa6r+s less than 6. More specifically, it is a partial ether obtained by condensation of a polyhydric alcohol such as glycol, glycerin, trimethylol propane, pentaerythritol, sorbitan or sorbitol, and a straight-chain or branched-chain, and saturated or unsaturated monool having 3-20 carbon atoms. Of those, a partial ether of glycerin, sorbitan or sorbitol, and monool having 10-20 carbon atoms is preferable, monoether is more preferable, and monoether of glycerin is particularly preferable.
In the lubricant for a refrigeration system of the present invention, the addition amount of alcohol compound of component (C) is not particularly limited, and may appropriately be selected in accordance with the situation. The amount is preferably 0.1-2.0% by weight, particularly preferably 0.2-1.0% by weight, on basis of the whole lubricant.
The benzotriazole derivative is a compound represented by the following formula (4); 
where R1, R2 and R3 represent hydrogen, an alkyl group having 1-20 carbon atoms or an aryl group having 1-20 carbon atoms, and may be the same or different. Benzotriazole is a compound that substituents bonding to nitrogen atom at the lowest portion in the formula (4) are hydrogen atom. It is assumed that metal surface is covered with those compounds so that the compounds have the function to protect metal material from corrosive substance such as ammonia refrigerant.
In the lubricant for a refrigeration system of the present invention, addition amount of the benzotriazole compound of component (D) is not particularly limited and may appropriately. be selected according to the situation. The amount is preferably 1-200 ppm by weight, particularly preferably 5-50 ppm by weight, to the whole lubricant.
Refrigerant used together with the lubricant for a refrigeration system of the present invention is ammonia refrigerant. This should be understood to be a refrigerant comprising ammonia. That is, such a refrigerant corresponds to not only a refrigerant consisting of ammonia, but two components-mixed refrigerant containing ammonia and low molecular weight hydrocarbon compound or ammonia and the above-mentioned fluorinated hydrocarbon, and three components-mixed refrigerant containing ammonia, low molecular weight hydrocarbon compound and the above-mentioned fluorinated hydrocarbon.
The lubricant for a refrigeration system of the present invention and ammonia refrigerant may be filled in appropriate proportion in accordance with the specification or manual of refrigeration system applied. Specifically, ammonia refrigerant/lubricant ratio for a refrigeration system by weight is in a range of preferably 99/1-1/99, more preferably 95/5-30/70.
If necessary, the lubricant for a refrigeration system of the present invention may optionally contain conventional lubricant base oils for a refrigeration system, such as naphthenic mineral oils or synthetic oils (e.g., alkylbenzene oils, ether oils, ester oils or fluorinated oils) and conventional additives. Examples of the additives include stabilizers such as phenylglycidyl ether or alkylglycidyl ether, extreme pressure agents such as tricresyl phosphate or triphenyl phosphate, and defoamers such as polydimethylsiloxane or polymethacryl acrylate. Further, conventional additives such as dispersants, viscosity index improvers, anti-rusts, corrosion inhibitors, pour point depressants can optionally be compounded. Those additives are generally mixed with the lubricant of the present invention in an amount of 10 ppm to 10% by weight.